Why is dsolve returning an arbitrary constant?
4 vues (au cours des 30 derniers jours)
Afficher commentaires plus anciens
David Winthrop
le 25 Nov 2019
Modifié(e) : David Goodmanson
le 25 Nov 2019
I have the following differential equation I want to solve from a simple harmonic motion problem.
When I enter this into MATLAB including two initial conditions, I get an arbitrary constant even though there should not be one. Why?
>> syms y(t) g L c
S = dsolve(diff(diff(y(t))) -L*y - g == 0, y(0) == c,diff(y(0))== 0)
S =
exp(-L^(1/2)*t)*(c - C5 + g/L) - g/L + C5*exp(L^(1/2)*t)
0 commentaires
Réponse acceptée
David Goodmanson
le 25 Nov 2019
Modifié(e) : David Goodmanson
le 25 Nov 2019
Hi David,
you need slightly different syntax.
syms y(t) g L c
Dy = diff(y)
S = dsolve(diff(diff(y(t))) -L*y - g == 0, y(0) == c,Dy(0)== 0)
S =
(exp(L^(1/2)*t)*(g + L*c))/(2*L) - g/L + (exp(-L^(1/2)*t)*(g + L*c))/(2*L)
Also, assuming k/m = w0^2 is positive as usual, then for harmonic motion the sign of the k/m term needs to change.
syms y(t) g c w0
Dy = diff(y)
S = dsolve(diff(diff(y(t))) +w0^2*y - g == 0, y(0) == c,Dy(0)== 0)
S =
g/w0^2 - (exp(-t*w0*1i)*(- c*w0^2 + g))/(2*w0^2) - (exp(t*w0*1i)*(- c*w0^2 + g))/(2*w0^2)
0 commentaires
Plus de réponses (0)
Voir également
Catégories
En savoir plus sur Calculus dans Help Center et File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!